Upgrade question

[rtk86]

I have a personally liable corporate plan with AT&T that provides us with a discount as well as waived termination fees. I called an AT&T representative and asked if they could move my upgrade date up since I can in theory terminate with no fees. She said she was unable to move my date up but suggested that I buy the iPhone on a new line at the discounted price. Then once it is activated, I can cancel my previous line. She said she didn't believe I could cancel the new line I added and that I would lose my phone number as well as my unlimited data plan. Is there a reason I wouldn't be able to just cancel the new line and move the phone to my original phone number and keep unlimited data?